This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 9702687-6 filed in Sweden on Jul. 11, 1997; the entire content of which is hereby incorporated by reference.
The present invention relates to a device and a method at printed boards for use in electronics systems.
A simple printed board according to prior art consists of a number of layers, wherein the lowest layer is termed support in the text below. The support is made of a suitable electrically conductive material, for instance brass, copper or aluminium. Transmission conductors, also termed conductors below, are etched out of an electrically conductive conductive pattern layer of the printed board, wherein a layer of dielectric material separates the conductive pattern layer frown the support. The conductors connect components on the printed board electrically to each other as desired.
An electromagnetic field occurs in a known manner between the conductors and the support of the printed board, wherein part the electromagnetic field is lost in the dielectric. This is specifically related to printed board assemblys used at high frequencies above 1 GHz, as energy losses can be significant and large amounts of heat is liberated in the conductors.
Examples of said problems with losses in the dielectric are at long transports of high frequency signals in the conductors, and communication between modules, so-called MCM (Multi Chip Modules). The modules, working independently at high frequencies, are mounted on a common so-called mother board. This board is made of a cheaper material, because the electronics on the mother board operates at low frequencies.
One known method for minimizing said losses occurring in the printed board assembly is to use a dielectric with good high frequency qualities.
A disadvantage with this method is that these dielectrics are expensive to use in the printed board assembly.
Another method according to prior art is to mill out a groove with air of the dielectric between the conductor and the support. The dielectric field from the conductor then passes through the air groove, implying remarkably decreased losses of the conductor compared to a solid dielectric.
A disadvantage with the method above is that it is complicated and requires long time to perform.
U.S. Pat. No. 3,904,997 discloses a conductor attached to a dielectric material. An electrically conductive ground plane, comprising a channel, has contact with the dielectric, so the conductor is enclosed in the channel with an air gap to the ground plane.
In U.S. Pat. No. 2,800,634 a method for the losses of a wave guide for instance on a printed board assembly operating at high frequencies is disclosed. Thereby, an air gap is employed between a ground plane and the wave guide, wherein a layer of dielectric material of the printed board is arranged to the ground plane and builds up the air gap between the ground plane and the conductor.
One problem that is solved by the invention is to obtain good transmission qualities in a non-expensive manner of conductors in a predetermined area of a printed board, in particular employed at high frequencies.
Thus, the object of the present invention is to obtain good transmission qualities in a non-expensive manner for transmission conductors at a predetermined area of printed boards.
To solve this problem, the present invention employs mounting of a separate component for signal transmission on a predetermined area where good transmission qualities on the printed board is required. An area of the component, facing the printed board, comprises a conductor, wherein air gap is obtained between the conductor and the printed board. The produced printed board with its component has an air gap which is well adapted to the conductor.
In more detail, the problem is solved as follows. The component comprises a layer of dielectric material, plated with an electrically conductive layer, and the conductor is etched out of this electrically conductive layer.
The printed board comprises a support of an electrically conductive material, wherein one layer of dielectric is attached to the support. Conductor patterns are etched out of an electrically conductive pattern layer on the dielectric layer. The printed board is on a predetermined area, requiring good transmission qualities, provided with a mounting surface for the component.
Subsequently, the component is mounts with the conductor facing the printed board, to the mounting surface of the printed board. Electrically conductive attachment joints, also termed attachment joints below, for instance soldering joints or joints of electrically conductive glue, connects each one of the outer parts of the conductor with corresponding pattern conductor on the printed board. The thickness of the attachment joints achieve herein an air gap between the conductor and the printed board.
According to another alternative embodiment of the invention, a groove is milled out of the dielectric layer of the printed board above, wherein the groove is arranged under the conductor, obtaining an enlarged air between the conductor and the printed board.
If yet better transmission qualities a required of an area of the printed board, the dielectric layer of the component can consist of a dielectric with good high frequency qualities.
An advantage of the present invention is that it is simple and non-expensive to use, since well-known standard materials can be employed. Only the component must if required be made of a more expensive material with good high frequency qualities.
An other advantage of the present invention is that good transmission qualities easily can be obtained at predetermined local places or areas of the printed board.
The invention will now be described in more detail illustrated by preferred embodiments of the invention and with reference to accompanying drawings.